In conjunction with projection displays, it is desirable to employ a color management system, and it is further desirable that such color management systems facilitate production of a high contrast image while accommodating a relatively high level of illuminating flux. Unfortunately, currently existing color management systems are capable of achieving increased contrast at practical levels of illuminating flux levels only by employing highly specialized materials, resulting in unreasonable increases in cost.
A color management system may function by first separating input light (e.g., white light) into a plurality of color channels traversing the visible spectrum (e.g. red, green and blue) then using the separate color channels to illuminate a plurality of corresponding microdisplays (e.g., LCoS microdisplays) and recombining the color channels to produce an output light (e.g., white light). Where it is desired to project an image in conjunction with the output light beam, spatial information may be superimposed on each of the color channels by the microdisplays prior to recombination. As a result, a full color image may be projected with the output light beam. As used herein, the terms “microdisplay,” “panel,” and “light valve” refer to a mechanism configured for receiving an incipient light beam, imparting spatial information in the light beam, and emitting a modified light beam comprising the incipient light beam and the spatial information. For example, model number DILA SX-070 manufactured by the JVC company of Japan.
Prior art color management systems have thus far proven unable to produce high contrast images at low cost without compromising their ability to maintain reasonable quantities of illuminating flux. This is due in part to use of solid “cube-type” polarizing beamsplitters for color separation and recombination. These polarizing beamsplitters are otherwise referred to as MacNeille prisms or cube polarizing beamsplitters. “Cube type” polarizing beamsplitters are inherently susceptible to thermal gradients that typically arise at high flux levels, often causing stress birefringence which results in depolarization of the light and a loss of contrast. As a result, where high contrast images are required, is has been necessary to use costly high-index, low-birefringence glass. Although this solution has proven effective to reduce birefringence at low levels of flux, it is expensive and exhibits reduced effectiveness at eliminating thermally induced birefringence at high flux levels (e.g., greater than approximately 500 lumens).
For example, FIG. 1 illustrates a prior art color management system 100, commonly known as the ColorQuad TM from Colorlink, in which four cube polarizing beamsplitters and five color selective retardation components are used to provide color separation and recombination. In accordance with this system, the input cubic polarizing beamsplitter receives an input light beam 120 and separates it into three components, a green component 121, a blue component 122, and a red component 123. The red component 123 receives spatial information from a red panel 133; the blue component 122 receives spatial information from a blue panel 132; and the green component 121 receives spatial information from a green panel 131. Finally, the output cubic polarizing beamsplitter recombines the red component 123 and blue component 122 with green component 121 to form a full color image 140. It should be noted that at high levels of light flux, cubic polarizing beamsplitter 110 becomes thermally loaded and necessarily distorts physically, causing stress birefringence, which results in depolarization of the light and a loss of contrast.
In an attempt to reduce the adverse effects of the use of cube polarizing beamsplitters, various attempts have been made to implement plate polarizing beamsplitters in place of cube configurations in color management systems. However, these attempts have given rise to other optical aberrations associated with the plate polarizing beamsplitters such as astigmatism.
Accordingly, it would be advantageous to have a color management system that could be used in high flux projection systems while simultaneously functioning in a wide range of thermal environments with reduced birefringence sensitivity and improved durability. It would further be advantageous to have a color management system that could achieve these objectives without requiring costly, high index, low birefringence glass or particular susceptibility to optical aberrations produced by polarizing beamsplitters in plate configurations.